Method and apparatus for measuring spectrograms



March 26, 1940. .1. s. FOSTER 2,195,168

METHOD AND APPARATUS FOR MEASURING SPECTROGRAMS Original 'Filed'oct. 6,1936 FIGI 35 JOHN STUART FOSTER INVENTOR.

Patented Mar. 26, 1940 PATENT OFFICE METHOD AND APPARATUS FOR MEASURINGSPEOTROGRAMS John Stuart Foster, wmmoum, Quebec, Canada, assignor toBausch & Lomb Optical Company, Rochester, N. Y., a corporation of NewYork Application October 6, 1986, Serial No. 104,253

Renewed November 25, 1939 7 Claims.

The present invention relates to measuring lines or portions of a wedgespectrogram. Here-- tofore, this hasv been done by measuring the lengthof each line or portion and finding the difier ence. In both thecontinuous and discontinu-= ous wedge spectrograms, the intensitydecreases from the bottom of the spectrogram to an extinction point atthe top and the lines of the discontinuous wedge spectrogram taper aswell. The measuring system or the prior art was therefore inherentlyuncertain and inaccurate because of the dinicultr of determining theexact extinc tion point of the line or portion of the spectro= gramunder consideration. I have iound that when two such lines or portionscan he moved relatively to each other, their extinction points can bebrought into juxtaposition with great accuracy. A'measure of the amountof relative movement is therefore an accurate measure oi the differencein the lengths of the two lines.

One of the objects of the present invention is to provide a newand'improved method and apparatus for measuring the difierence in thelengths of the lines or portions of a wedge spectrogram. Another objectis to provide a method and apparatus for measuring the difference in thelengths of the lines of a discontinuous wedge spectrogram in whichadjacent images of the lines are formed in a view field and one of theimages is displaced to bring the tapered ends of the lines intojuxtaposition. A further object is to provide a method and apparatus formeasuring the difference in the lengths of different selected portionsof a continuous wedge spectrogram m which artificial lines are formedfrom the selected portions and the lengths of these artificial linesmeasured. These and other objectsand advantages reside in certain novelfeatures of construction, arrangement. and combination of parts andprocesses as will hereinafter be more fully set forth and pointed out inthe appended claims.

Referring to the drawing: Fig. l is a front elevation of a deviceembodying the present invention.

Fig. 2 is a view of the image displacing system, taken on line 22 ofFig. l. I

Fig. 3 is a view of the image field as it appears to the observer. a

Fig. 4 is a view of a typical discontinuous wedge spectrogram. x

Fig. 5 is a fragmentary view of a modification for measuring continuouswedge spectrograms.

Fig. 6 is a view of the image field of the modiflcation shown in F1g. 5.

Fig. '7 is a view of a typical continuous wedge spectrogram showing themasking diaphragms in place.

One form of apparatus for measuring the lines of a discontinuous wedgespectrogram according to the present invention is illustrated in thedrawing wherein it designates a discontinuous wedge spectrogram supportabove which are mounted two oppositely facing, right angle prisms ii andif? which direct the light irom the discontinuous spectrogram it to twolenses it and it, respeo= tively. The prism it and lens it are rigidlymounted in fixed relation on a slide it"; which can. he moved in adirection parallel to the plane or the spectrogram ill by means of ascrew ii. The prism l2 and lens it are similarly mounted on a slide itsimilarly controlled by a screw it. The lenses it and it are such thattheir principal ioci lie in the plane of the spectrogram it andtherefore the movement of the slides l5 and it will have no efiect onthe focusing of the lenses it and it.

From the lenses l3 and it, the light passes to two right angle prisms'ltand 20, respectively,

' where the light is twice reflected and directed respectively, to twocontiguous right angle prisms 23 and 24, respectively. The lenses 2! and22 have their principal foci in the exit faces of the prisms 23 and 24which prisms form a split image field. Since the lens systems l3, 2| andit, 22 have their principal foci always in the ob- Ject and imageplanes, the movement of the lenses l3 and it does not change either thelocation or size of the images.

In order to displace one image in the direction of the length of thespectrogram line, the lens 22 is mounted in a slide'25 which is movableacross the optical axis under the control of a screw 26. A pointer orvernier 21 on the slide 25 cooperates with a scale 28 to determine theextent of movement of the slide 25.

Y As shown in Fig. 4, the lines of the usual dis- 30, for some purposesuch as quantitative analysis, the prisms l I and I2 are positioned overthese lines and the images 29' and 30' are formed in the image field 3i.The lens 2.2 is then moved by means oi! the screw 26 until the images29' and 30' are in juxtaposition as indicated by the dotted outline inFig. 3. The amount of displacement oi! the image can then be read fromthe scale 28.

Figs. 5, 6 and '7 illustrate the modifications oi the above-describedapparatus necessary for measuring the lengths of different selectedportions of a continuous wedge spectrogram. In this modified form of theapparatus, two artificial lines 32 and 33 are formed from the continuouswedge spectrogram 34 by means of the slots 35 and 36 in the twodiaphragm plates 31 and 38, respectively. The diaphragm plate 31 issecured to the slide l5 by a bracket 39 so that its slot 35 is inalignment with the prism ii and the diaphragm plate 38 is similarlysecured to the plate l6 by the bracket 40. The brackets 39 and 0 may, ofcourse, be removabiy secured on the plates I5 and it so that theapparatus may be readily converted from one form to the other. Theoptical systems of both forms are identical in construction andoperation.

The artificial lines 32 and 33 formed from two selected portions of thecontinuous spectrogram are imaged at 32' and 33' in the image field 4i.These images 32 and 33' are dark at the bottom and their intensitydecreases to extinction points at the top and, as in the case of thelines of the discontinuous spectrogram, one image is displaced until theextinction points of the two images are in juxtaposition. The amount ofdisplacement is then the difference in the lengths of the two artificiallines.

From the foregoing it will be apparent that I am able to attain theobjects oi my invention and provide a new and improved method andapparatus for measuring the difierence in the lengths of portions of awedge spectrogram. In the claims the term "line" can designate eitherthe line of the discontinuous spectrogram or the artificial line formedfrom the continuous spectrogram by means of a diaphragm plate. Thestructure of the optical system is set forth merely as an example andvarious modifications can readily be made without departing from thespirit of my invention or the scope of the appended claims.

I claim:

l. The method of measuring the difference in length between two lines ofa wedge spectrogram, each having an extinction point at one end and abase at the other, which method comprises forming parallel adjacentimages of the two lines. displacing one of said images in the directionof its length until the images of the extinction points of the two linesare in immediately adjacent relation, and determining the distancebetween the images of the bases of said lines.

2. The method of measuring the difference in length between two selectedportions of a continuous wedge spectrogram comprising forming from achof said portions an artificial line having a base at one end and anextinction point at the other, forming adjacent parallel images of thetwo lines, displacing one of said images in the direction of its lengthuntil the images of the extinction points of the two lines are inimmediately adjacent relation, and determining the distance between theimages of the bases of said lines.

' 3. An apparatus for measuring the diil'erencc in length between twoselected lines of a wedge spectrogram, each line having an extinctionpoint at one end and a base at the other, comprising a support for aspectrogram, selection means movable longitudinally oi. the spectroramsupport and in alignment with said support for selecting the lines whosedifference in length is to be determined, means in alignment with saidselection means for forming parallel adjacent images of the two selectedlines, means for displacing one of the images relative to the other inthe direction of its length until the images of the extinction points ofthe two lines are in immediately adjacent relation, and means fordetermining the distance between the images of the bases of the twolines.

4. An apparatus for measuring the diflerence in the lengths of twoselected portions 01' a continuous wedge spectrogram comprising aspectrogramsupport, means in alignment with said support for formingfrom each of said portions an artificial line having a base at one endand an extinction point at the other, means for forming adjacentparallel images 01' the two artificial lines in a common observationfield, means for displacing the image of one of said lines in thedirection of its length relative to the image of the other line untilthe images of the extinction points of the two lines are in immediatelyadjacent relation, and means for measuring the distance between theimages of the bases of the two lines.

5. An apparatus for measuring the difference in length between two linesof a wedge spectrogram comprising a spectrogram support, two opticaltrains, each train comprising a'reflector for receiving light from aspectrogram on the support and reflecting it in a direction parallel tothe plane of the support and at right angles to a line of a spectrogramon the support, a lens adjacent the reflector and having its principalfocus at the plane, of a spectrogram on the support, means for movingthe lens and reflector along the axis of the reflected ray, and a secondlens for receiving light from the first-named lens to form an image of aline 01 a spectrogram on saidsupport, means for combining the rays from'both optical trains at an observation field, means for displacing theimage formed by one optical train relative to the image formed by theother optical train in the direction of the length of the image, andmeans for measuring the amount of such displacement. 6. A device formeasuring the difference in the lengths 01' two selected portions oi acontinuous wedge spectrogram comprising a spectrogram support, twoparallel narrow linear diaphragms movably mounted above said support sothat they extend across a spectrogram positioned on said support, meansfor moving said diaphragms to the selected portions of said spectrogram,two optical systems in alignment one with each diaphragm for formingadjacent parallel images of the portions outlined by said diaphragms,means for displacing one of said images relative to the other in thedirection of its length until its top is in immediately adjacentrelation with the top of the other image. and means for measuringv theamount of such displacement.

7. A device for determining the difference in the lengths of two linesof a wedge spectrogram each having an extinction point at one end and abase at the other comprising 'a spectrogram support, an optical systemfor iorming an image 01' one line oi a-spectrogram on said support, amovable optical system for forming an image of a second line of aspectrogram" on said support parallel to the image of the first line,means for moving said movable system transversely oi the lines of aspectrogram .on said support for selecting the line to be compared withthe line imaged by the first optical system, an observation field, meansfor directing the images from both optical systems to adjacent parallelportions of said observation field and means for displacing the lineimage formed by one optical system relative to the other line image inthe direction of the length of the line image.

JOHN STUART FOSTER.

